Not a native speaker, but I don't find any problem! However, I'd write - The only invariant to me is 'change.' I'd not put the article.
– Maulik V♦Jun 8 '18 at 8:16

You might add the context and where you are using this. I don't think invariant is generally used. I would write: "The only constant for me is change." In any case, change is a quality and not a countable noun, so no article is used..
– user3169Jun 9 '18 at 1:55